Battery powered entertainment and portable test equipment has become increasingly popular. The convenience of this portability is, however, partly offset by the need to continuously charge or recharge batteries. Proper circuit design can yield acceptable battery life for most portable appliances. It is primarily the accidental or inadvertent act of leaving the instrument on for unintentionally long periods of a time that is the bane of battery operated equipment. The relatively high cost of today's sophisticated batteries produces a need for conservation circuits which can prevent inadvertent battery drain. Some entertainment devices such as television sets, stereo systems, and radios incorporate a "sleep" switch which will turn off the instrument after a predetermined period of time. Sleep timers or battery saver circuits have not been generally available for retrofitting into existing electronic products. The greatest benefit in the use of such devices would occur with traditional miniaturized consumer products such as tape players, radios, radio receivers and related goods. Adding battery saving circuitry to such existing products is not only difficult because of size and packaging constraints, but is well beyond the technical expertise of most consumers. Existing technology uses either a switch to be momentarily depressed and released to start a timing process, or an additional switch on the circuitry to be actuated.
One such device uses a timing circuit wherein after a switch within the timing circuitry is closed, power will be supplied for only a predetermined time. Such an assembly is disclosed in U.S. Pat. No. 3,940,660 issued Feb. 24, 1976 in the name of Frederick H. Edwards. This patent discloses a timing circuit wherein after a switch is closed, power will be supplied for only a predetermined time. By moving the switch to its ON position, any charge on a timing capacitor will be discharged turning a second switch ON to supply power to the device which and will remain ON until the timing capacitor has charged to a magnitude greater than a preset magnitude. This type of assembly requires a switch within the timing circuitry additional to the electrical device's switch for operating the timing control. A problem with this type of assembly is that such an assembly would not easily be adapted to a preexisting electrical device whose consumer desires a timer turn off circuit. The patent requires an additional switch integral with the timing circuitry. Adaptation of the circuitry and additional switch to an existing electrical device is complex and difficult.
Another such device uses a switch which needs to be momentarily depressed to initiate a timing cycle. Such a device is disclosed in U.S. Pat. No. 3,965,743 issued Jun. 29, 1976 in the name of Robert Bruce Turner and assigned to American Medical Electronics Corportation. A problem with this type of device is that the switch needs to be momentarily depressed or, turned on and off. In the consumer setting where the subject invention is to be used, this type of device is not adequate since the timing cycle will not initiate if the switch is merely turned on.
U.S. Pat. No. 4,777,384, issued Oct. 11, 1988 to Altenhof discloses a timing device which is inserted between an energizing control switch and a load. An AC source voltage is applied to the energizer control switch and the load. The device operates in a plurality of modes, and more important are the modes identified by version 3. Upon energizing after a long duration of the switch deenergized, a timed mode is entered. The load initially energizes until expiration of the timer, then deenergizes. Upon energizing after a short duration deenergized, the continuous mode is entered. The load is energized for as long as the device is energized. The device does not utilize a battery power supply which applies DC power, interconnection of the control means between the battery and the energizing switch nor entrance in the timing mode independent of prior openings of the device or energizing switch.
U.S. Pat. No. 4,740,672, issued Apr. 26, 1988 to Takei discloses a cooking apparatus with a timer function. The cooking device includes a timer, computer and start key. The operator sets the timer, and when a user depresses the cooking start key the microcomputer commands the heating control to begin cooking. Cooking is stopped when the display content is "zero". The apparatus does not include a battery powered supply for supplying DC power wherein the control circuit interconnects same to the device, nor connection of the control circuitry between the battery and the device which contains the device switch, nor subsequent opening and reclosure of the device switch closes the electronic switch means to reinitiate the predetermined time.